Path arrangement for parison heating

ABSTRACT

Preformed hollow parisons are received on vertically disposed pins attached to an endless chain which conveys these parisons through a heating oven and out at a point spaced away from the side walls of said oven. After the parisons have traveled though the oven and been heated to the desired temperature, the pins are rotated 90* so as to transfer the parisons to a horizontal position. These horizontally disposed parisons are then ready to be received by a molding station. A preferred apparatus for accomplishing the transfer of the parisons from a vertical to a horizontal position comprises a support base to which the support pins are fixedly attached, this base being hinged at one end to a flange extending upwardly from a link plate on the chain; a cam follower fixedly attached to the other end of this base; and a stationary cam plate. The support base is biased so as to support the support pin in a vertical position by a spring or spring clip; as the chain advances the cam follower contacts the stationary cam plate; this cam follower riding against the cam plate causes the support base to pivot about the hinge so as to rotate the support pin from a vertical to a horizontal position, and then as the cam follower passes the high point on the cam plate the base is rotated back so as to return the support pin to a vertical position.

United States Patent l Inventor William KillSlOW, .llr- PrimaryExaminer-1ohn J. Camby Kansas y, Mo. Anorney-Young and Quigg [21] AppLNo. 875,081 [22] Filed Nov. 10, 1969 [45] Patented Dec. 14, 1971ABSTRACT: Preformed hollow parisons are received on ver- [73] AssigneePhillips Petroleum Co n tically disposed pins attached to an endlesschain which con- Continuatlon-inart a li ati s N veys these parisonsthrough a heating oven and out at a point 696,329,Jan. 8, 1968, nowPatent Nb, spaced away from the side walls of said oven. After the3,477,700, Thi li ti N 10, 19 9 parisons have traveled though the ovenand been heated to the Ser. No. 875,081 desired temperature, the pinsare rotated 90so as to transfer the parisons to a horizontal position.These horizontally disposed parisons are then ready to be received by amolding [54] PATH ARRANGEMENT FOR PARISON HEATING station. A preferredapparatus for accomplishing the transfer CMmFJ Drawing 8 of the parisonsfrom a vertical to a horizontal position com- 52 us. Cl 263/8 3 basewhich Pins m fiwdly [51 1 Int Cl 9/24 tached, this base being hinged atone end to a flange extending [50] Field of Search 263/8, upwardly froma link plate on the chain; acam follower fixedly 18 [DIG attached to theother end of this base; and a stationary cam plate. The support base isbiased so as to support the support 56] Ref r n Cit d pin in a verticalposition by a spring or spring clip; as the chain UNITED STATES PATENTSadvances the cam follower contacts the stationary cam plate;

this cam follower riding against the cam plate causes the supg 'gg' al263/8 port base to pivot about the hinge so as to rotate the support$283 046 ll/l966 D W 263/8 X pin from a vertical to a horizontalposition, and then as the 3'477'7O0 I H1969 I m a ISIDIG 39 cam followerpasses the high point on the cam plate the base is ms 263/8 rotated backso as to return the support pin to a vertical position.

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PATH ARRANGEMENT FOR IPARHSON HEATING CROSS-REFERENCE TO RELATEDINVENTION BACKGROUND OF THE INVENTION This invention relates to aprocess and apparatus for heating a preformed hollow parison.

While the blow-molding art goes back over 100 years, it has only been inthe last years that the blow molding of hollow plastic articles hasachieved significant commercial success. With this expanded utilizationof blow-molding techniques has come progressively more rigorousrequirements from the purchasers of the finished product with regard tothe appearance, durability, chemical resistance, low cost, and the likeof the product.

It is a well-known fact that many polymers which are particularlysuitable for blow molding such as the olefin polymers, undergo thephenomenon known as orientation when stretched in the solid state at atemperature below the crystalline melt point. Since this orientation canresult in as much as a -fold increase in tensile strength, it was onlynatural that attempts should be made to utilize this phenomenon in theproduction of blow molded hollow articles such as bottles. Since thegreatest orientation occurs at a temperature just below the crystallinemelt point while the polymer is on a heating cycle, it was earlyrecognized that little orientation could be effected in a conventionalblow-molding operation wherein a molten parison was extruded betweenmold halves and blown; first the temperature of the parison could not becontrolled close enough, and second the slight orientation achieved waspredominantly in the circumferential direction since at best only aminor amount of stretching in the longitudinal direction occurred. Onemethod of achieving the desired product is to extrude or mold a hollowparison preform, cool it to room temperature, carefully reheat it tojust below its crystalline melt point, and then transfer it to a moldingstation where it is grasped at both ends. stretched longitudinally, thusimparting orientation in a longitudinal direction, and thereafter placedquickly in a mold and expanded to conform to the shape of the mold bythe introduction of fluid pressure into the interior of the parison,thus stretching it circumferentially to impart orientation in a seconddirection. Such a procedure achieves a product of exceptional strength,and surprisingly, in the case of materials such as polypropylene,greatly improved optical properties.

However, since the optimum temperature for orientation is that justbelow the crystalline melt point of the material comprising thethermoplastic parison, it is apparent that special care must be taken inheating and in transferring the parison to the molding station so as toachieve uniform heating of the parison and so as to transfer parisonwhich is at a temperature just below its crystalline melt point, withoutin any way damaging it. A simple and economical method of heating hollowparisons would be simply to pass the parisons through a circulating airoven. However, since the parisons are going to be heated to atemperature just below their crystalline melt point there is a problemof distortion of the parisons during this heating step if they are nothandled carefully. By placing the parisons around vertically disposedsupporting pins they can be moved through the heating oven and uniformlyheated without distortion due to sagging. In many instances, however,for instance where the blowing station is horizontally disposed, or ininstances where the blowing station is vertically disposed but theparison is moved into position in the blowing station by grasping itwhile in the horizontal position and rotating it 90, it is necessarythat the parison be received from the heating zone in a horizontalposition.

Also, because of the relatively narrow temperature range at whichmaximum orientation can be achieved, even the slight temperaturevariation near the walls of an oven can cause a sufficient variation inthe temperature of the parisons as they pass out of the oven as to giveerratic results in the finished item. Even if the heating fluid in anair oven has uniform flow, exposure of one side of the parison to anoven wall of a different temperature during the last pass before itexits from the oven results in uneven heating.

SUMMARY OF THE INVENTION It is an object of this invention to providefor heating a preformed hollow parison while in a vertically disposedposition and thereafter to transfer said parison to a horizontalposition preparatory to being received by a molding station. It is afurther object of this invention to provide for heating a preformedhollow parison in an air oven to a temperature just below itscrystalline melting point and thereafter transferring said parison intoposition for being received by a molding station, without damaging saidparison, and it is yet a further object to provide more uniform heatingof a parison in an oven.

In accordance with this invention an endless chain is positioned withina heating oven, said chain having support means affixed thereto.Preformed hollow parisons are loaded onto these pins and conveyed in awinding; path through the oven and out at a point spaced apart from thesidewalls of said oven to heat said parisons to a temperature below themelt point of the thermoplastic material comprising the parison.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. l is a plan view with portionsbroken away showing the preferred embodiment of the heating oven andparison transfer mechanism;

FIG. 2 is a view partially in section of a support base carrying aparison; and

HO. 3 is a plan schematic view of an alternative chain arrangement.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The novel heating oven andparison transfer mechanism of the instant invention can be used in theheating of hollow thermoplastic parison preforms made, for instance, ofany orientable thermoplastic materials such as polymers of at least one1- olefin, said l-olefm having two to eight carbon atoms per molecule,poly(vinyl chloride) and the like. It is especially useful in theheating of parisons made of polymers of l-olefins selected from thegroup consisting of ethylene, propylene, butene and mixtures thereof,more particularly polypropylene.

These polymers can be formed into hollow parison preforms and cooled toa temperature below their crystalline freezing point. These hollowparison preforms in the solid state are then heated to a temperature ofabout l to about 50, preferably 5 to 25 F. below their melting point(crystalline melting point in the case of crystalline polymers) in anoven while disposed in a vertical position and thereafter transferred toa horizontal position preparatory to delivery to a molding station. Atthis molding station these parisons are generally stretchedlongitudinally to impart longitudinal orientation; they are then causedto expand to conform to the shape of a mold by the application of apressure differential between the interior of the parison and the moldwall thus imparting circumferential orientation to give a biaxiallyoriented product. This orientation process imparts as much as a 20-foldincrease in tensile strength to the plastic material.

The crystalline melt point can be determined by heating a small piece ofthe plastic under a polarizing microscope. The specimen is heated slowlyand the temperature at which birefringence disappears is the crystallinemelt point.

While the polymer at the temperature for achieving maximum orientationstill contains a certain amount of crystallinity and thus has thegeneral physical appearance of solid polymer as opposed to being in afluid, easily moldable, condition, it is apparent that, at a temperatureof 1 to 50 F. below the crystalline melt point, a considerable amount ofthe crystallinity has disappeared and the parison cannot be subjected torough handling.

The preformed hollow parison can be formed initially with one closed endand one open end and the open end placed over the supporting pins in theheating oven, or the parison preforms at this stage can simply besections of pipe or tubing which are open at both ends and which areclamped or pinched off at one end after delivery to the molding station.

By the term molding station" as used throughout the specification andclaims is meant either a single station where the heated parison isintroduced into a mold and expanded by means of differential fluidpressure or a two or three stage molding station wherein the parison isfirst stretched longitudinally to impart longitudinal orientation andthen introduced into a mold and caused to conform to the shape of themold by introduction of fluid pressure into the interior of the parison.

The oven will generally be of the circulating air type with blowers tocirculate the air vigorously. Thennostats capable of controlling thetemperature within i3 F., preferably within i-l" F., are used since hotspots and wide temperature fluctuation cannot be tolerated when it isdesired, as here, to heat the polymer to just below its crystalline melttemperature. Other heating means such as radiant heaters can also beemployed. Thus, the invention is also applicable to heating with aninfrared means where the sidewalls also cause a temperature variation.

Referring now to FIG. I there is shown a heated air oven with the topportion partially cut away so as to show the endless chain 12 and theparison transfer station I4. Spaced along this endless chain are supportbases 17 made of heat resistant plastic. Each support base is attachedto a link plate of said chain by means of hinge l8. Upstanding from saidsupport base is vertically disposed support pin 20. Projecting inwardlyfrom said support base is cam follower 22. Affixed atop top wall 24 ofoven 10 is parison loading mechanism 26 which is simply a funnel in thisembodiment. Thus, the parisons are near a sidewall of the oven on entrythereto which is satisfactory since temperature variations in theparison at this point are of no consequence. As endless chain 12 isincrementally advanced forward as shown by the arrow, a support base 17is positioned under parison insertion mechanism 26, and a parison isdropped into place over vertically disposed support pin 20. At the sametime an identical support base carrying parison 28 is moved from undersaid parison insertion mechanism, and another identical support base 17is rotated about hinge 18 so as to transfer parison 28 to a horizontalposition for delivery from'the heating zone to a molding station. As canbe seen from FIG. I, parison 28 emerges from the oven at a point spacedapart from the sidewalls. Thus, during the critical final heating time,the parison travels through an area nearer the center of the oven spacedapart from the sidewalls where the temperature is not affected byconduction through the sidewalls and thus is more uniform.

Referring now to FIGS. I and 2, support base 17 is hinged to flange 30which is attached to chain link plate 32. FIG. 2 shows a support base 17carrying a parison 28 in a vertical position and thus reflects theposition of these elements as they approach the parison transfer station14, this position being designated by the character A in FIG. 1. Base 17is biased in a horizontal plane, so as to position support pin in avertical position, by spring 34. It is apparent that a spring clip orother means of biasing the support pin in a vertical position can beemployed; thus the term spring" as used herein is intended to includecoil springs, flat metal spring clips and the like.

It is highly preferred that the portion of internal support pin 20 whichtouches the parison be made of low coefiicient of friction, low thermalconductivity material such as polytetrafluorethylene. Preferably thestatic coefficient of friction against solid polyethylene, for instance,is less than about 0.5, more preferably less than about 0.25, mostpreferably less than about 0.1. Preferably the thermal conductivity kvalue of the material comprising this washer is less than 3.9, morepreferably less than 1. By k value is meant the standard k value inBTU/(hr.)(ft.)'(F./inch). By using such a material the parison slideseasily onto and off of the supporting pin and does not stick to washer36. The support base is preferably made of a similar material to that ofthe washer so that the parison cover is in contact with no metal whilein the heating zone. Contact of the parison preform while in the heatingzone with any metal part which stays within the heating zone isundesirable since the metal, being a high thermal conductivity material,would transfer an excessive amount of heat into the parison at thepoints of contact, thus causing distortion and sticking. As shown inFIG. 2, a washer 36 of Teflon TFE (Registered Trademark) is affixed tothe upper portion of vertically disposed support pin 20 and serves toform the point of contact between the parison and the support pm.

As the endless chain approaches sprocket 38, cam follower 22 on base 17engages cam sloping surface 39 on the cam plate which is stationary andis carried by the oven by means not shown. As the chain continues itstravel around sprocket 38, base 17 is rotated to a vertical plane thusrotating support pin 20 carrying parison 28 to a horizontal position asthe cam follower reaches the highest point on cam surface 39. The chaincarried by sprockets 44, 46, 48, 50, 52, and 54 in addition to sprocket38 advances forward in discrete increments, controlled by a conventionalindexing mechanism such as a Geneva type, such that it stops with asupport base 17 at the transfer station in the position shown in FIG. I.The parison is then removed from support pin 20 through aperture 43 inoven 10 and delivered to a molding station (not shown). As the chainmoves forward again, cam follower 22 passes the high point on cam plate42 and support pin 20 is returned to a vertical position through theaction of rail 41. As can be seen from FIG. 1, cam follower 22 is raisedto a position between the cam plate and rail 41 by the action of slopingcam surface 39. It is then returned to a horizontal position by theaction of rail 41. Since FIG. 1 is a plan view, the parison supportcarrying a heated parison which is shown approaching the parisontransfer station 14 (position A) from the interior portion of the ovenand the identical support shown leaving this station (position B) alongthe sidewall of the oven look somewhat similar. However, it can beseenby the position of the shade lines that in the first instance theinterior of a cylinder (parison 28) is being viewed and in the second,washer 36 and the base 17 itself are being viewed. This support base,now in the position designated by the character B is ready to receiveanother parison when it moves under parison loading mechanism 26.

Parison loading mechanism 26 can comprise a clamping mechanism forholding one end of a parison, said clamping mechanism being attached toan air cylinder which pushes the parison downward over the supportingpin at the appropriate time, or it can simply be a hollow cylinder intowhich the parisons are fed and directed to fall by the force of gravityover one of the vertically disposed supporting pins or a funnel asshown.

To conserve heat, a sliding door or the like can cover the opening tothe parison loading station and the aperture 43 during the portion ofthe cycle where no parison is being loaded or unloaded.

Referring now to FIG. 3, there is shown an alternative arrangement ofthe chain wherein parisons are introduced into oven 10a at loading meansor station BB, pass through as shown by the arrows, and exit fromessentially the center at unloading means or station AA.

Many standard parts such as temperature controllers, bolts, clamps, andthe like, have not been shown for the sake of simplicity but theirinclusion is understood by those skilled in the art as is within thescope of the invention.

EXAMPLE Propylene homopolymer having a density of 0.905 (ASTM Dl505-63T), a melt index of 2 (ASTM D l238-62T, Condition L) and acrystalline melting point of 340 F. was extruded into tubing having aninternal diameter of 0.8 inch and a wall thickness of 0.15 inch. Thistubing was cooled to room temperature and cut into 5 inch lengths. These5 inch lengths of tubing were positioned over vertically disposedsupporting pins having a Teflon washer at the upper end thereof, saidpins being carried by an endless chain, and conveyed through an air ovensuch as is shown in MG. l in which they were heated to a temperature of320 to 338 F. The chain contained about 2410 support pins and advancedat 6 second intervals to give a total heating time of 24 minutes foreach parison. These heated parisons, while at a temperature of 2 tobelow their crystalline melting point were transferred from a verticalto a horizontal position by a parison transfer mechanism, such as isshown in N68. l and 2, and received by a blow-molding station where theywere stretched longitudinally, placed in a mold cavity, and expanded byintroduction of internal fluid pressure so as to cause them to conformto the shape of the mold. The resulting biaxially oriented bottles wereuniform in appearance indicating that the parison had not been damagedor distorted during the heating or transfer operations.

While this invention has been described in detail for the purpose ofillustration it is not to be construed as limited thereby but isintended to cover all changes and modifications within the spirit andscope thereof.

I claim:

ll. Apparatus comprising in combination:

an oven;

an endless chain having support means for carrying thermoplasticparisons on a winding path through said oven;

a parison loading means; and

a parison unloading means, said chain being so disposed that it passesadjacent a first sidewall toward a backwall on a first path, over afirst sprocket and along a backwall toward a second sidewall on a secondpath, around a second sprocket and along said second sidewall toward afront wall on a third path, around a third sprocket and back toward saidbackwall along a fourth path spaced inward from said third path, arounda fourth sprocket and toward said first sidewall along a fifth pathspaced inward from said second path, around a fifth sprocket and backtoward said front wall along a sixth path spaced inward from said firstpath, around a sixth sprocket and back toward said backwall along aseventh path spaced inward from said sixth path, and around a seventhsprocket toward said front wall along an eighth path separated from saidfirst sidewall by paths 1, 6 and 7 and separated from said secondsidewall by paths 3 and Al.

2. Apparatus according to claim ll wherein said chain on said final passemerges from essentially the center between said sidewalls.

3. Apparatus according to claim l wherein said oven is an air oven.

d. Apparatus according to claim ll wherein said parison loading means isdisposed so as to introduce said parisons onto said chain as said chainpasses adjacent said first sidewall of said oven.

5. Apparatus according to claim A wherein said support means comprisesvertical pins.

6. A method of heating a thermoplastic parison to molecular orientationtemperature comprising introducing said parison into a heating zone andpassing said parison adjacent a first wall of said heating zone toward abackwall of said heating zone on a first path, along said backwalltoward a second sidewall on a second path, along said second sidewalltoward a front wall along a third path, back toward said backwall alonga fourth path spaced inward from said third path, toward said firstsidewall along a fifth path spaced inward from said second path, backtoward said front wall along a sixth path spaced inward from said firstpath, back toward said backwall along a seventh path spaced inward fromsaid sixth path, and back toward said front wall along an eighth pathseparated from said first sidewall by said first, sixth and seventhpaths and separated apart from said second sidewall by said third andfourth paths.

7. A method according to claim 6 wherein said path along which saidparison is passed out of said heating zone is essentially in the centerof said heating zone.

8. A method according to claim 6 wherein said thermoplastic material isa polymer of at least one l-olefin said I- olefin having two to eightcarbon atoms per molecule and said orientation temperature is l-50 F.below the crystalline melting point thereof.

9. A method according to claim 6 wherein said thermoplastic ispolypropylene and said orientation temperature is 5-25 F. below thecrystalline melting point thereof.

10. A method according to claim 6 wherein said parison is introducedinto said heating zone along said first sidewall thereof.

1. Apparatus comprising in combination: an oven; an endless chain having support means for carrying thermoplastic parisons on a winding path through said oven; a parison loading means; and a parison unloading means, said chain being so disposed that it passes adjacent a first sidewall toward a backwall on a first path, over a first sprocket and along a backwall toward a second sidewall on a second path, around a second sprocket and along said second sidewall toward a front wall on a third path, around a third sprocket and back toward said backwall along a fourth path spaced inward from said third path, around a fourth sprocket and toward said first sidewall along a fifth path spaced inward from said second path, around a fifth sprocket and back toward said front wall along a sixth path spaced inward from said first path, around a sixth sprocket and back toward said backwall along a seventh path spaced inward from said sixth path, and around a seventh sprocket toward said front wall along an eighth path separated from said first sidewall by paths 1, 6 and 7 and separated from said second sidewall by paths 3 and
 4. 2. Apparatus according to claim 1 wherein said chain on said final pass emerges from essentially the center between said sidewalls.
 3. Apparatus according to claim 1 wherein said oven is an air oven.
 4. Apparatus according to claim 1 wherein said parison loading means is disposed so as to introduce said parisons onto said chain as said chain passes adjacent said first sidewall of said oven.
 5. Apparatus according to claim 4 wherein said support means comprises vertical pins.
 6. A method of heating a thermoplastic parison to molecular orientation temperature comprising introducing said parison into a heating zone and passing said parison adjacent a first wall of said heating zone toward a backwall of said heating zone on a first path, along said backwall toward a second sidewall on a second path, along said second sidewall toward a front wall along a third path, back toward said backwall along a fourth path spaced inward from said third path, toward said first sidewall along a fifth path spaced inward from said second path, back toward said front wall along a sixth path spaced inward from said first path, back toward said backwall along a seventh path spaced inward from said sixth path, and back toward said front wall along an eighth path separated from said first sidewall by said first, sixth and seventh paths and separated apart from said second sidewall by said third and fourth paths.
 7. A method according to claim 6 wherein said path along which said parison is passed out of said heating zone is essentially in the center of said heating zone.
 8. A method according to claim 6 wherein said thermoplastic material is a polymer of at least 1 1-olefin said 1-olefin having two to eight carbon atoms per molecule and said orientation temperature is 1*-50* F. below the crystalline melting point thereof.
 9. A method according to claim 6 wherein said thermoplastic is polypropylene and said orientation temperature is 5*-25* F. below the crystalline melting point thereof.
 10. A method according to claim 6 wherein said parison is introduced into said heating zone along said first sidewall thereof. 